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Simultaneous Particle Tracking and Temperature Measurements during Additive Manufacturing using a High-speed Spectral Plenoptic Camera
Get PDFIn this work, a high-speed spectral plenoptic camera was used for three-dimensional (3D) simultaneous particle tracking and pyrometry measurements of hot spatter particles ejected during the metal additive manufacturing process. Additive manufacturing (AM) has an increasing role in the aerospace, energy, medical and automotive industry (DebRoy et al., 2018). While this new technology enables the production of highly advanced parts, research on the fundamental mechanisms governing the laser-matter interactions are an ongoing challenge because of the spatial and temporal resolution inherent to the AM process. One challenge is the characterization of spatter particles ejected from the melt pool, as these particles can be incorporated into the final part affecting the mechanical properties (Deng et al., 2020). One potential solution for simultaneously measuring velocity and temperature of the spatter particles is the spectral plenoptic camera
Plunging jets from orifices of different geometry
Get PDFPlunging jets are used in many industrial and civil applications, as for example in sewage and water treatment plants, in order to enhance aeration and mass transfer of volatile gases. They are also observed in natural processes as rivers self-purification, waterfalls and weirs.
Many investigations dealt with the plunging jets in different configurations, but the dependence on Reynolds number and jet geometry were still not sufficiently addressed. For example, Mishra et al. (2020) studied an oblique submerged water impinging jet at different nozzle-to-plate distances and impingement angles, but only at a rather small Reynolds numbers (2600). On the other hand, different jet geometries have been extensively considered, but not for the plunging jet configuration (Mi, 2000; Hashiehbaf &Romano, 2013).
In this work, plunging water jets issuing in air from orifices of different shape are considered. The aim of the work is to detail and compare jet behaviors in terms of velocity fields generated after impacting the air-water interface, as a function of Reynolds number and orifice geometry. However, air bubbles entrainment is mainly avoided in order to study the jet characteristics in a simpler case and use it as a reference starting point for future works
Enhanced functional binning for one- and two-point statistics using a posteriori Uncertainty Quantification of LPT data
Get PDFIn the evaluation of Lagrangian particle tracking (LPT) measurement data the use of spatially binned flow statistics in the form of one, two or multi-point statistics is often an essential step towards better understanding of the measured flow fields. Increasingly there is a focus towards uncertainty quantification of the measurement system however these evaluations are seldom used to directly improve the statistics by directly involving them into the calculation. We present our Functional Binning approach which makes use of such uncertainty information as a core component for the calculation of improved statistics. The improvements towards prior approaches are shown utilizing synthetic data as well as data from a real-world subsonic jet experiment. Beyond the initial formulation for one-point statistics, we show that this approach is readily extended towards two-point statistics and explore more advanced utilizations of uncertainty information for the optimal selection of particle pairs. Furthermore, the benefits of more individualized particle error estimations are investigated and some strategies for archiving such information are investigated
An Intensity-based and a lifetime-based PSP imaging method with enhanced sensitivity
Get PDFA pressure-/temperature-sensitive paint (PSP/TSP) has been developed and used as a measurement tool for the two-dimensional distribution of pressure and temperature on aerodynamic surfaces. In recent years, although the concern with measuring a pressure difference of several Pa, such as countermeasures against the noise of small fans, has been growing, the resolution of current PSP measurements is limited to several 10 Pa, even with carefully conducted measurements. For highly accurate measurements, researches on the advanced coating films in PSP/TSP have eagerly been conducted to date. However, measurement resolution and accuracy deteriorate when quantum efficiency or lifetime decrease under high pressure or high temperature conditions
Color contamination matrix property assessment for improvement of colored smoke PIV
Get PDFA single-camera color PIV system that can acquire PIV data of three separated layers has been redesigned, purposing improvement of wind tunnel applicability. We target smoke image that has particle-per-pixel values higher than unity. The system constitutes of a high-power color-coding illuminator and a digital color high-speed video camera. RGB values in recorded image involves severe color contaminations due to five optical and digital sequences (Fig. 1). To quantify this, a snapshot calibration is proposed to describe the contamination matrix equation (Eq. (1)). Taking the inverse matrix (Eq. (2)) allows in-plane PIV in each color layer to be accurately implemented. We also derive mathematical limits to operate the colored smoke PIV, which is explained by the matrix property (Eq (3)). Feasibility of the proposed method has been demonstrated by application to a turbulent wake behind a Delta wing (Fig. 2) and also to a boundary layer flow along heated chocolate
Investigation of Best Practices in Volumetric Reconstruction for Plenoptic PIV
No full textThis paper investigates the effect of smoothing operation in 3D reconstruction using a plenoptic camera. A plenoptic camera - also known as light field camera - features a commercial off the shelf camera with added microlens array (MLA) behind the imaging lens, directly in front of the sensor. The main lens focuses the light to the MLA plane, where each microlens then re-directs the light to small regions of pixels behind, each pixel corresponding to different angle of incident (T. Fahringer (2015)) (Adelson and Wang (1992)). Thus, MLA encodes angular information of incident light rays into the recorded image that assist to acquire 4D information (u,v,s,t) of light-field including both position and angular information of light rays captured by the camera (Ng et al. (2005)) (Adelson and Wang (1992))
Application of simultaneous time-resolved 3-D PTV and Two Colour LIF in Studying Rayleigh-Benard Convection
Get PDFTo study the flow topology and temperature distribution of Rayleigh-Benard convection in a highly slender cell, measurement of the simultaneous velocity and temperature in the 3-D domain is required. For this aim, implementing a simultaneous time-resolved 3-D PTV and two-colour PLIF is planned. As a part of this development, for both PTV and two-colour PLIF techniques, the experimental setup has been implemented separately to measure time-resolved 2-D velocity and temperature and is presented in this paper. For PTV, a scanning system is also utilized to scan the flow field to capture the planar velocity in different depths of the flow domain. Progress on calculation of the out-of-plane velocity component including the theory is discussed. Finally, results of the time-resolved 2-D PTV and PLIF systems are presented
TrackAER: Real-Time Event-Based Particle Tracking
Get PDFEvent-based cameras (Lichtsteiner et al., 2008; Posch et al., 2010; Gallego et al., 2020) operate fundamentally different from frame-based cameras: Each pixel of the sensor array reacts asynchronously to relative brightness changes creating a sequential stream of events in address-event representation (AER). Each event is defined by a microsecond-accurate time stamp, the pixel position and a binary polarity indicating a relative increase or decrease of light intensity. Thus, event-based cameras only sense changes in a scenery while effectively suppressing static, redundant information. This renders the camera technology promising also for flow diagnostics. In established approaches like PIV or PTV vast amounts of data are generated, only for a large part of redundant information to be eliminated in data post-processing. In contrast, eventbased cameras effectively compress the data stream already at the source. To make full use of this potential, new data processing algorithms are needed since event-based cameras do not generate conventional framebased data. This work utilizes an event-based camera to identify and track flow tracers such as helium-filled soap bubbles (HFSBs) with real-time visual feedback in measurement volumes of the order of several cubic meters
An experimental approach to analyze aerosol and splatter formation in a dental practice
Get PDFThe flow velocity, trajectories, and size distribution of droplets produced during a dental scaling procedure using a Cavitron ultrasonic scalar (CUS) has been investigated by optical flow tracking velocimetry and shadowgraphy measurements. The droplet sizes are found to vary from 5 -500 µm; these correspond to droplet nuclei that could carry viruses. The droplet velocities also vary between 0.7 m/s and 1.3 m/s. These observations confirm the critical role of aerosols in the transmission of disease during dental procedures, providing invaluable knowledge for developing protocols and procedures to ensure the safety of both dentists and patients especially during COVID-19 pandemic
An Experimental Study to Quantify the Rotor-to-Rotor Interaction Characteristics of a Small Unmanned-Aerial-Vehicle
Get PDFThe flow interactions between laterally aligned rotors were investigated experimentally to study the rotor-to-rotor interactions on the aerodynamic and aeroacoustic performance of small unmanned aerial vehicles (UAVs). Two identical rotors, similar to the dimensions of Phantom 3 (DJI), were mounted separately on different stages in a wide-open space. High-accuracy force and sound measurements were conducted to document the thrust and noise at various separation distances. The detailed flow structures and corresponding vortex evolutions behind the rotors were resolved clearly by using high-resolution PIV measurements. As the rotor separation distance decreased, intensified flow interactions were noted within the rotors. More specifically, the twinrotor with separation distance of L= 0.05D exhibited a significantly enhanced thrust fluctuation (i.e., ~ 240% higher) and augmented noise level (i.e., ~ 3dB) in comparison with that of baseline case. Measured PIV results indicated that a strong recirculation region existed near the top-right of the twin-rotor case, which is believed to be the reason for the increased thrust fluctuations and aeroacoustic noise level